Interleukin 8 (IL8) is a member of the chemokine family and is produced by a wide range of cell types like monocytes, macrophages, fibroblasts and ceratinocytes. It primarily mediates the activation and migration of neutrophils from peripheral blood into tissue and is involved in the initiation and amplification of inflammatory processes, which occur in the human immune system in response to a wide variety of pathogens 1. Thus IL8 play an important role in inflammatory lung diseases like bronchial asthma or severe infections caused by respiratory syncytial virus (RSV).

RSV, a single-stranded RNA virus, is involved in at least 70% of cases of infectious infantile bronchiolitis and has been repetitively linked to asthma. It has been hypothesized that severe RSV infection in infancy might lead to the development of recurrent wheezing and/or bronchial asthma 23, and consequently a common genetic background of both diseases has been discussed 4. According to the current evidence, genetic and environmental factors determine the type of immune response to RSV infection. Furthermore, this response may affect the development of control mechanisms in the regulation of airway diseases, mainly bronchial asthma.

Increased concentrations of IL8 have been described in the bronchoalveolar fluid and sputum of asthmatic patients 5. In addition, repeated administration of IL8 into the airways induces bronchial hyperreactivity in guinea pigs 67. Genetic association of IL8 has been described with asthma 8 and RSV bronchiolitis 910.

IL8 binds with high affinity to two different receptors: IL8 receptor alpha (IL8RA, CXCR1) and beta (IL8RB, CXCR2). These closely related proteins are members of the superfamily of receptors, which couple to guanine nucleotide binding proteins. IL8RA is localized on chromosome 2q35 11, where linkage to total serum IgE levels in asthmatics has been described 12. In addition, association of IL8RA polymorphisms has recently been described with asthma and chronic obstructive pulmonary disease 13.

We were interested in the relationship between severe RSV infection and/or bronchial asthma and IL8 and IL8RA polymorphisms in the German population. We chose to study two IL8 promoter polymorphisms (-251A/T and -781C/T) and three amino acid variants in IL8RA (M31R, S276T and R335C), which are located in the N-terminus of the protein, in the third extracellular loop and in the C-terminus of the protein respectively. The selection of the IL8 polymorphisms was based on previous studies in our asthmatic and control populations, in which these polymorphisms were shown to be most informative 8.

So far, only few studies have investigated the impact of polymorphisms within the IL8 signaling pathway on the genetic background of severe RSV associated diseases or bronchial asthma. The IL8 pathway includes IL8 itself, its two receptor chains IL8RA and IL8RB and its degradative enzyme aminopeptidase N 20. In a previous study, we have shown that IL8 polymorphisms are in association with bronchial asthma in the German population using 230 asthmatic children and 270 randomly chosen controls 8. Furthermore, we hypothesized that polymorphisms within IL8 have opposite effects on the development of asthma and severe RSV infections. The hypothesis was based on the observation that the -251T allele was more common in patients with asthma than in controls. In contrast, two studies from Hull and colleagues have demonstrated that the opposite allele, that is -251A, is associated with severe RSV infection in the English population 910.

Thus the first aim of the current study was to test whether our initial hypothesis of an opposite role of IL8 polymorphisms on asthma and RSV infections holds in a population of German children with severe RSV associated diseases. Second, we wanted to verify the association between bronchial asthma and IL8 polymorphisms in an extended asthmatic population (increased by 90 asthmatic children to 320 probands). Thirdly, we extended our investigation to include IL8RA as recently association of asthma and chronic obstructive pulmonary disease with this gene has been reported in another German samples 13.

In the here presented study, the polymorphisms -251A/T and -781C/T within IL8 showed no association with severe RSV associated diseases - neither in analyses of single polymorphisms nor in haplotype analyses. This might suggest that IL8 does not play a major role in the development of severe RSV infections in the German population. These findings are in contrast to the above mentioned studies of Hull et al. 910. The discrepancy could be due to several reasons: The infants included in the study of Hull et al. were younger than in our study. Furthermore, the inclusion criteria differed slightly between both studies, for example, Hull and colleagues included children with pre-existing heart diseases, whereas we excluded those children. Finally, though the English and German population represent both Caucasians it is well known that the genetic predisposition to allergic diseases are at least partially different between Germans and English people 21.

The association between bronchial asthma and -781C/T within IL8 could be confirmed in an extended asthmatic population (p = 0.011), whereas the association with the second IL8 polymorphism -251A/T and asthma became weaker and was no longer statistically significant (p = 0.087). This might be in accordance to one study, showing that -251A/T has no functional impact, whereas the base pair substitution C to T at position -781 within the IL8 promotor enhances the binding of transcription factors and thus is probably more important in the genetic regulation of IL8 expression 22.

Furthermore, a direct comparison of the asthmatic population with the RSV population revealed significant differences, both for -781C/T alone (p = 0.034) as well as in the haplotype analyses (p = 0.005). These results may support our initial hypothesis, that polymorphisms within IL8 have opposite effects in the pathophysiology of asthma and RSV associated diseases. However, one should notice, that the allelic frequencies of the polymorphisms did not markedly differ between controls and children with severe RSV infections. Thus the positive association might merely reflect the fact that the genotype frequencies in asthmatics differ from controls.

In contrast to Stemmler et al, who found that the IL8RA polymorphisms M13R and R335C were significantly associated with bronchial asthma 13, we found no association of these polymorphisms neither with asthma nor severe RSV associated diseases. Again the conflicting results might be due to different inclusion criteria. The study by Stemmler et al. used 68 adult patients and 130 children with asthma whereas we used exclusively children with asthma. The "adult phenotype" of asthma is quite different from the asthmatic phenotype in children. For example pediatric asthma is much more often allergic than asthma in adults. Thus it might not be surprising that the genetic background of asthma differs between adults and children 23. Furthermore, the size of our asthmatic study population was larger than the population of Stemmler et al. (198 asthmatic patients versus 320 patients). Thus the significant result in their study might just reflect a type 1 error. However, as the risk factor conferred by a single gene is quite small in complex genetic diseases like asthma, it is also possible that we missed true association in our population due to a type 2 error.

We conclude from our data, that IL8 might play a role in the genetic predisposition to bronchial asthma and that these effects are different, or maybe even opposite to the effects of the same polymorphisms on severe RSV associated diseases. In contrast IL8RA polymorphisms do not play a major role, neither in the development of severe RSV infections nor in asthma.

The author(s) declare that they have no competing interests.

BP performed genotyping and sequencing of IL8 polymorphisms as well as the statistical analyses and drafted the manuscript.

MK participated in the clinical design of the study and the recruitment of the RSV population.

JH performed genotyping and sequencing of IL8RA polymorphisms

JF participated in the clinical design of the study.

AH conceived and coordinated the study and helped to draft the manuscript.

All authors have read and approved the final manuscript.